1. Field of the Invention
The invention relates to electron beam heating systems and, particularly, to an electron beam heating system having carbon nanotubes.
2. Discussion of Related Art
Generally, a conventional electron beam heating system includes a field emission electron source. The field emission electron source has a conducting cathode with a tapered tip that is powered with a negative voltage relative to a nearby conducting anode. Although the electron beam heating systems have proven sufficient to heat materials in macroscopic applications, the high power cost, low current density and large spot size limit their microscopic application.
Carbon nanotubes (CNTs) produced by means of arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. length/diameter ratios) (greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features tend to make CNTs ideal candidates for field emission electron sources.
A electron beam heating system has been disclosed. In this electron beam heating system, the single CNT is used as field emission source. When a distance between the field emission electron source and the object is about 100 micrometers, a voltage applied to the field emission electron source is about 1000Y, but only 2 microamperes of current can be emitted therefrom. Further, the controllability of the electron beam heating system is less than desired, because single CNT is so small in size.
What is needed, therefore, is an electron beam heating system having carbon nanotubes, which has high field emission efficiency, and is easily and controllably manufactured.